It works in large biomes as well though then the island is the size of a small continent and you spawn on three small sandbars with no trees (and no saplings in the bonus chest) 750 blocks or so to the south east.

"-2433212456887413774" seems very good in large biomes, true you spawn in the middle of the ocean but a bonus chest will give you plenty of wood for a boat.

Traveling 650 blocks straight east will get you to the island which is, of course, pretty large but mostly sand, the whole island is about 350 blocks long but the central green island in an island is only 100 blocks across.